1. Field of the invention
The present invention relates generally to a system for detecting the amount of crop material present in an agricultural machine, and more particularly to a system using one or more acoustic sensors which can be used for detecting the amount of crop lost from a harvester, as well as the amount of crop yielded by the harvester.
2. Description of the Related Art
An agricultural combine, also referred to as a harvester, is a vehicle used to gather a crop from a field once the crop has reached maturity. The combine is driven through a field, and the plants (crop) in that field are pulled into an attachment called a header on the front of the machine. As the plants are pulled into the header, they are cut and fed into a threshing unit internal to the combine. In general terms, the threshing unit forces the cut plants to be rubbed between a rotating drum, or rotor, and a concave surface in order to separate the nutrient component (such as grain) from the remainder of the plant (the chaff). Most of the separated grain falls below the drum to a set of sieves, and then through the sieves where it is collected and transported via an elevator to a grain tank. The chaff material is passed over a series of conveyors called “straw walkers” which move the chaff toward the back of the machine. Air is blown through the sieves and the straw walkers, and the chaff is blown up off of the straw walkers and out the back of the combine. Some additional grain that remains in the chaff as it moves over the straw walkers, being heavier than the chaff and less susceptible to the blowing air, will fall through into the sieves to be collected in the grain tank.
The settings on the combine, and in particular the settings of the sieves in the combine, can, if not properly adjusted, cause amounts of grain to be lost out the back of the combine along with the chaff, resulting in lower crop yields. In addition, factors such as the speed of the combine through the field, ambient environmental conditions, crop moisture content, and crop type can affect the amount of crop that is lost during the harvesting process. In order to know how to adjust the combine settings properly, the operator needs to have an indication of how much crop is being lost at any given moment. This information is typically gathered through the use of a grain loss sensor, which is capable of detecting when crop material is being lost out the back of the combine, and can distinguish crop material from waste material (such as chaff).
A typical grain loss sensor utilizes a piezoelectric pad or membrane, typically located at the back of the sieves where material is falling or being blown out of the combine. Although both grain material and chaff material are ejected from the back of the combine, the grain is generally heavier and falls closer to the back of the machine, while the lighter chaff is blown farther away. The piezoelectric pad is placed close to the back of the machine, pad facing up, such that falling crop or kernels of grain, rather than chaff, will strike the pad. When the kernels impact the sensor, the deformation of the piezoelectric pad generates a measurable voltage due to piezoelectric effect, which electrical signals can be detected and interpreted as the presence of lost crop material.
Piezoelectric grain loss sensors suffer from several disadvantages. Since a portion of the piezoelectric pad has to be deformed by the grain strikes in order to be detected, the piezoelectric material must cover the entire surface where detection is required. However, to cover the entire width of the back of a combine, a very large piezoelectric pad would be required to cover the span and depth of the area. This would result in a very expensive sensor. Instead, combine manufacturers typically install two or three smaller sensors in key areas at the rear of the vehicle where the heaviest flow of material is expected. As a combine moves and tilts while operating on a sloping surface, the sensors often move out of these expected material flow zones, and the grain loss rates measured are artificially low.
Also, since a direct strike is required, the piezoelectric material itself must be exposed to the elements, and is exposed not only to being struck by grain, rocks, and other material, but also to the direct sun, precipitation, dust, and extremes in temperature. As a result, the sensors must frequently be cleaned, repaired, and replaced.
Existing piezoelectric sensors have a very limited ability to distinguish between types of material hitting their surfaces. Most of these prior art sensors will count a pebble or rock hit as a grain hit. This also limits the ability of the piezoelectric sensors to provide accurate loss rates.
The ideal technology for implementing a grain loss sensor would be flexible enough so that it could be adapted for use as a yield sensor in the same combine. A yield sensor is used to measure the amount of material that is harvested and successfully captured in the grain tank. This information is best captured in real-time, as an amount of material or flow rate, so that yield mapping applications can be implemented. A yield-mapping application combines information on the instantaneous flow rate of material with location information (such as that from a GNSS system such as GPS) to create a map showing amount of material (yield) mapped to specific locations in the field. The yield map can then be used by the farmer or operator to determine where and in what amounts to apply chemicals (such as fertilizers, pesticides, etc.) to boost the overall output of the field.
Unfortunately, a piezoelectric sensor is not well suited for measuring yield. The piezoelectric sensor could be placed at the top of the clean grain elevator, where grain is delivered (typically by chain-driven paddles moving up an enclosed elevator shaft). However, the amounts of material hitting the piezoelectric sensor would quickly overwhelm the sensitivity capabilities of the sensor, and the constant pummeling of material against the pad would likely damage or wear out the sensor quickly. Some combines use mechanical means for sensing yield, such as causing a flap to be pushed open to varying degrees by the material flowing into the grain tank based on the amount of material present. These mechanical sensing means for yield are inaccurate and subject to breakdown.
What is needed in the art is a new type of material sensing technology which can overcome the limitations described above associated with piezoelectric sensors, yet which is flexible enough to allow it to be adapted for use in yield sensing.